Active matrix organic electroluminescent display and fabricating method thereof

ABSTRACT

An active matrix organic electroluminescent display device includes a first substrate and a second substrate facing and spaced apart from each other, a thin film transistor on an inner surface of the first substrate, a first electrode connected to the thin film transistor, an organic electroluminescent layer on the first electrode, a second electrode on the organic electroluminescent layer, a passivation layer on the second electrode, a black matrix on an inner surface of the second substrate, the black matrix includes a plurality of open portions, a color filter layer at the plurality of open portions, a color changing layer on the color filter layer, an overcoat layer on the color changing layer, and an adhesive film between the passivation layer and the overcoat layer.

[0001] The present invention claims the benefit of the Korean PatentApplication No. P2001-87707 filed in Korea on Dec. 29, 2001, which ishereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an organic electroluminescentdisplay device, and more particularly, to an active matrix organicelectroluminescent display device including a thin film transistor and afabricating method thereof.

[0004] 2. Discussion of the Related Art

[0005] A cathode ray tube (CRT) has been commonly used as a displayscreen for devices such as televisions and computer monitors. However, aCRT has the disadvantages of being large, heavy, and requiring a highdrive voltage. As a result, flat panel displays (FPDs) that are smaller,lighter, and require less power have grown in popularity. Liquid crystaldisplay (LCD) devices, plasma display panel (PDP) devices, fieldemission display (FED) devices, and electroluminescent display (ELD)devices are some of the types of FPDs that have been introduced inrecent years.

[0006] An ELD device may either be an inorganic electroluminescentdisplay device or an organic electroluminescent display (OELD) devicedepending upon the source material used to excite carriers in thedevice. OELD devices have been particularly popular because they havebright displays, low drive voltages, and can produce natural colorimages incorporating the entire visible light range. Additionally, OELDdevices have a preferred contrast ratio because they areself-luminescent. OELD devices can easily display moving images becausethey have a short response time of only several microseconds. Moreover,such devices are not limited to a restricted viewing angle as other ELDdevices are. OELD devices are stable at low temperatures. Furthermore,their driving circuits can be cheaply and easily fabricated because thecircuits only require a low operating voltage. In addition, themanufacturing process of OELD devices is relatively simple.

[0007] In general, an OELD device emits light by injecting electronsfrom a cathode electrode and holes from an anode electrode into anemissive layer, combining the electrons with the holes, generating anexciton, and transitioning the exciton from an excited state to a groundstate. Since the mechanism by which an OELD produces light is similar toa light emitting diode (LED), the organic electroluminescent displaydevice may also be called an organic light emitting diode.

[0008] In an organic electroluminescent display device, multiple organicelectroluminescent layers may be used in which each layer emits redlight, green light, or blue light in order to display full color images.Because any of the organic electroluminescent layers may break down overthe course of time, it may be difficult to maintain the range of allpossible colors when the organic electroluminescent display device hasbeen driven for a long period of time. To solve this problem, a methodof displaying full color images by using a single organicelectroluminescent layer for all pixels and a color changing medium hasbeen suggested in U.S. Pat. No. 5,294,870, which are hereby incorporatedby reference. This method will be illustrated in FIGS. 1 to 3.

[0009]FIG. 1 is a plan view of an organic electroluminescent displaydevice according to the related art. In FIG. 1, a planarization layer101 is formed on a substrate, and a plurality of first electrodes R1-R5,which are spaced apart from each other, are formed on the planarizationlayer 101 along a first direction. An organic electroluminescent layer 8is formed on the plurality of first electrodes R1-R5. The organicelectroluminescent layer 8 is electrically connected to the plurality offirst electrodes R1-R5. A plurality of second electrode portions C1-C6,which are spaced apart from each other, are formed on the organicelectroluminescent layer 8 along a second direction that issubstantially perpendicular to the first direction. Each secondelectrode portion C1-C6 includes three sub-electrodes “a,” “b” and “c.”The second electrode portion C1-C6 crosses the first electrode R1-R5,thereby defining pixel regions, of which a representative pixel regionis “P.” The pixel region “P” includes three sub-pixel regions “Rp,” “Gp”and “Bp” of red, green and blue that are defined by the sub-electrodes“a,” “b” and “c” and the first electrodes R1-R5. External signals areapplied through a peripheral portion “A” where the electroluminescentlayer 8 is not formed.

[0010]FIG. 2 is a cross-sectional view of the organic electroluminescentdisplay device of FIG. 1 taken along II-II according to the related art.FIG. 3 is a cross-sectional view of the organic electroluminescentdisplay device of FIG. 1 taken along III-III according to the relatedart.

[0011] In FIGS. 2 and 3, green color changing medium “G” and red colorchanging medium “R” are formed on a substrate 2. The green and red colorchanging media “G” and “R” correspond to green and red sub-pixel regions“Gp” and “Rp,” respectively. The green and red color changing media “G”and “R” may be made of a material not susceptible to a photolithographicprocess. Next, a planarization layer 4 is formed on the green and redcolor changing media “G” and “R” to planarize a surface of the substrate2 and separate adjacent green and red sub-pixel regions “Gp” and “Rp.”The planarization layer 4 is made of transparent insulating materialthrough a spin coating method or a solgel method without an additionalpatterning process. The planarization layer 4 also protects the greenand red color changing media “R” and “G.” Next, a plurality of firstelectrodes “R1” and “R3” are formed on the planarization layer 4. Theplurality of first electrodes “R1” and “R3” are made of transparentconductive material such as indium-tinoxide (ITO) to transmit light.

[0012] Next, a sidewall 6 is formed on the plurality of first electrodes“R1” and “R3” at a boundary of the green and red sub-pixel regions “Gp”and “Rp.” The sidewall 6 may be formed through depositing and patterningphotoresist. The sidewall 6 may be made of silicon oxide (SiO₂), siliconnitride (SiN_(x)) or aluminum oxide (Al₂O₃). Next, an organicelectroluminescent layer 8 is formed on the sidewall 6 and the pluralityof first electrodes “R1” and “R3.” The organic electroluminescent layer8 is made of a material emitting blue light. A plurality ofsub-electrodes “a,” “b” and “c,” which function in combination as asecond electrode, are formed on the organic electroluminescent layer 8.Preferably, the plurality of sub-electrodes “a,” “b” and “c” are made ofa material having a low work function so that each is substantiallyefficient for proper operation of the electroluminescent display device.When the plurality of sub-electrodes “a,” “b” and “c” are formed througha sputtering method, the positioning of a target including a sourcematerial is important in order that the plurality of sub-electrodes “a,”“b” and “c” are properly spaced. If the target is close to a firstsurface “X” of the sidewall 6, the source material is deposited on thefirst surface “X” of the sidewall 6, but the source material is notdeposited on a second surface “Y” of the sidewall 6 and a portion of theorganic electroluminescent layer 8 adjacent to the second surface “Y.”Accordingly, the organic electroluminescent layer 8 has a gap betweenthe adjacent sub-electrodes “a,” “b” and “c” along a first direction.

[0013] The organic electroluminescent display device of FIGS. 1 to 3 isa passive matrix organic electroluminescent display device. In thepassive matrix organic electroluminescent display device, scan lines aresequentially driven so that the brightness of each pixel may beappropriately determined. Accordingly, the brightness for which a pixelis driven should be the multiple of the desired average brightness andthe number of scan lines required to obtain the desired averagebrightness. Thus, as the number of scan lines increases, the requiredsupply voltage and supply current increase as well. An increase in therequired supply voltage and supply current accelerates the degradationof a device and increases the power consumption of the device. Althougha passive matrix organic electroluminescent display device may beadequate for small display devices, it is not an adequate solution inlarger display devices.

SUMMARY OF THE INVENTION

[0014] Accordingly, the present invention is directed to an organicelectroluminescent display device and a fabricating method thereof thatsubstantially obviate one or more of the problems due to limitations anddisadvantages of the related art.

[0015] An object of the present invention is to provide an organicelectroluminescent display device that produces color of a high quality,consumes a relatively low amount of power and permits a large displayscreen, and a fabricating method thereof.

[0016] An object of the present invention is to provide an organicelectroluminescent display device whose elements have substantiallyequivalent expected life spans by forming one organic electroluminescentlayer over an entire surface of a substrate and emitting light through acolor changing medium and a fabricating method thereof.

[0017] Another object of the present invention is to provide an organicelectroluminescent display device that can be protected from an externalimpact by forming a thin film transistor and a color changing mediumover different substrates and attaching the respective substrates and afabricating method thereof.

[0018] Additional features and advantages of the invention will be setforth in the description which follows, and in part will be apparentfrom the description, or may be learned by practice of the invention.The objectives and other advantages of the invention will be realizedand attained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

[0019] To achieve these and other advantages and in accordance with thepurpose of the present invention, as embodied and broadly described, anactive matrix organic electroluminescent display device includes a firstsubstrate and a second substrate facing and spaced apart from eachother, a thin film transistor on an inner surface of the firstsubstrate, a first electrode connected to the thin film transistor, anorganic electroluminescent layer on the first electrode, a secondelectrode on the organic electroluminescent layer, a passivation layeron the second electrode, a black matrix on an inner surface of thesecond substrate, the black matrix includes a plurality of openportions, a color filter layer at the plurality of open portions, acolor changing layer on the color filter layer, an overcoat layer on thecolor changing layer, and an adhesive film between the passivation layerand the overcoat layer.

[0020] In another aspect, A method of fabricating an organicelectroluminescent display device includes steps of forming a thin filmtransistor on a first substrate, forming a first electrode connected tothe thin film transistor, forming an organic electroluminescent layer onthe first electrode, forming a second electrode on the organicelectroluminescent layer, forming a passivation layer on the secondelectroluminescent layer, forming a black matrix on a second substrate,the black matrix has a plurality of open portions, forming a colorfilter layer at the plurality of open portions, forming a color changinglayer on the color filter layer, forming an overcoat layer on the colorchanging layer, and bonding the first substrate to the second substrateby interposing an adhesive film between the passivation layer and theovercoat layer.

[0021] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory and are intended to provide further explanation of theinvention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which are included to provide afurther understanding of the invention and are incorporated in andconstitute a part of this specification, illustrate embodiments of theinvention and together with the description serve to explain theprinciple of the invention. In the drawings:

[0023]FIG. 1 is a plan view of a related art electroluminescent displaydevice;

[0024]FIG. 2 is a cross-sectional view of the organic electroluminescentdisplay device of FIG. 1 taken along II-II according to the related art;

[0025]FIG. 3 is a cross-sectional view of the organic electroluminescentdisplay device of FIG. 1 taken along III-III according to the relatedart;

[0026]FIG. 4 is a cross-sectional view of an exemplary organicelectroluminescent display device according to the present invention;

[0027]FIGS. 5A to 5D are cross-sectional views of an exemplary method offabricating a first substrate for an organic electroluminescent displaydevice according to the present invention; and

[0028]FIGS. 6A to 6D are cross-sectional views of an exemplary method offabricating a second substrate for an organic electroluminescent displaydevice according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Reference will now be made in detail to the preferred embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings.

[0030]FIG. 4 is a cross-sectional view of an exemplary organicelectroluminescent display device according to the present invention. InFIG. 4, a first substrate 100 and a second substrate 200 may face and bespaced apart from each other. A thin film transistor (TFT) “T” includinga gate electrode 121, an active layer 131 of silicon, a source electrode122, and a drain electrode 123 may be formed on an inner surface of thefirst substrate 100. A first passivation layer 140 may be formed on theTFT “T.” The first passivation layer 140 may have a drain contact holeexposing the drain electrode 123 and may be composed of either inorganicinsulating materials or organic insulating materials. A first electrode150 of an opaque conductive material may be formed on the firstpassivation layer 140. An organic electroluminescent layer 160 emittingblue light may be formed on the first passivation layer 140. The organicelectroluminescent layer 160 may cover an entire surface of the firstsubstrate 100. A second electrode 170 composed of a transparentconductive material, such as indium-tin-oxide (ITO) or indium-zinc-oxide(IZO), may be formed on the organic electroluminescent layer 160. Asecond passivation layer 180 may be formed on the second electrode 170.

[0031] A black matrix 220 may be formed on an inner surface of thesecond substrate 200. The second substrate 200 may be made of atransparent material, such as glass or plastic. The black matrix 220 maybe placed in a position corresponding to a TFT “T” and may have aplurality of open portions 225. A color filter layer 230, includingfirst, second, and third sub-color filters 231, 232, and 233, may beformed at the plurality of open portions 225. For example, the first,second, and third sub-color filters 231, 232, and 233 may correspond tored, green, and blue, respectively. Alternatively, a differentcombination or order of sub-color filters may be used. Each of thefirst, second, and third sub-color filters 231, 232, and 233 may beformed at one open portion 225.

[0032] A color changing layer 240, including first and second colorchanging mediums 241 and 242, may be formed on the color filter layer230. In FIG. 4, the first color changing medium 241, which may changecolor to red, may be formed on the first subcolor filter 231, and thesecond color changing medium 242, which may change color to green, maybe formed on the second sub-color filter 232. An overcoat layer 250 maybe formed on the color changing layer 240. Subsequently, an adhesivefilm 300 may be interposed between the second passivation layer 180 andthe overcoat layer 250. The adhesive film 300 may be used to bond thefirst and second substrates 100 and 200 together.

[0033] Accordingly, an organic electroluminescent layer that emits bluelight may be formed over an entire surface of a substrate and light maybe emitted using the first and second color changing mediums of red andgreen. Since a thin film transistor may be used to drive an organicelectroluminescent display device, a larger display device producing ahigher quality display with reduced power consumption may be obtained.In addition, a transparent adhesive film may be attached to the organicelectroluminescent layer that may shield and protect the organicelectroluminescent layer from moisture and oxygen without optical loss.As a result, reliability may be improved. Furthermore, since a firstelectrode is made of an opaque conductive material and a secondelectrode is made of a transparent conductive material, light may beemitted toward the second substrate having a color changing layer.

[0034] A method of fabricating an organic electroluminescent displaydevice according to an embodiment of the present invention isillustrated in FIGS. 5A to 6D.

[0035]FIGS. 5A to 5D are cross-sectional views of an exemplary method offabricating a first substrate for an organic electroluminescent displaydevice according to the present invention. FIGS. 6A to 6D arecross-sectional views of an exemplary method of fabricating a secondsubstrate for an organic electroluminescent display device according tothe present invention. In FIG. 5A, a thin film transistor (TFT) “T” maybe formed on a first substrate 100. The TFT “T” may include a gateelectrode 121, an active layer 131 of silicon, a source electrode 122,and a drain electrode 123. Preferably, the active layer 131 is made ofpolycrystalline silicon. The first substrate 100 may be made of glass orplastic, and may have a thickness of about 0.7 mm.

[0036] In FIG. 5B, a first passivation layer 140 may be formed on theTFT “T” through depositing and patterning organic or inorganicinsulating materials. The first passivation layer 140 may include adrain contact hole that exposes the drain electrode 123. The organicinsulating material may be composed of silicon nitride (SiN_(x)) orsilicon oxide (SiO₂). The inorganic insulating material may be composedof benzocyclobutene (BCB) and photo acryl.

[0037] In FIG. 5C, a first electrode 150 may be formed on the firstpassivation layer 140 through depositing and patterning an opaqueconductive material, such as metal. The first electrode 150 may beconnected to the drain electrode 123 of the TFT “T” through the draincontact hole.

[0038] In FIG. 5D, an organic electroluminescent layer 160 emitting bluelight may be formed on the first electrode 150. A second electrode 170that may be made of a transparent conductive material, such asindium-tin-oxide (ITO) or indium-zinc-oxide (IZO), may be formed on theorganic electroluminescent layer 160. A second passivation layer 180 maybe formed on the second electrode 170. The second passivation layer 180may also be made of organic or inorganic insulating materials.

[0039] In FIG. 6A, a black matrix 220 may be formed on a secondsubstrate 200. The black matrix 220 may have a plurality of openportions 225. The second substrate 200 may be made of a transparentmaterial, such as a glass or a plastic, and may have a thickness ofabout 0.5 mm.

[0040] In FIG. 6B, a color filter layer 230 including first, second, andthird sub-color filters 231, 232, and 233 may be formed at the pluralityof open portions 225. The first, second, and third sub-color filters231, 232, and 233, respectively corresponding to red, green and blue,may be formed sequentially through, for example, a pigment dispersionmethod, a dyeing method or an inkjet method. Here, each of the first,second, and third sub-color filters 231, 232, and 233 may be formed atone open portion 225.

[0041] In FIG. 6C, a color changing layer 240 including first and secondcolor changing mediums 241 and 242 may be formed on the color filterlayer 230. Here, the first color changing medium 241 that changes thecolor of light passing through it to red may be formed on the firstsub-color filter 231, and the second color changing medium 242 thatchanges the color of light passing through it to green may be formed onthe second subcolor filter 232. Preferably, a sum of the thickness ofthe first sub-color filter 231 and the thickness of the first colorchanging medium 241 may be equal to the sum of the thickness of thesecond sub-color filter 232 and the thickness of the second colorchanging medium 242. Moreover, each of these sums may be equal to thethickness of the third sub-color filter 233.

[0042] In FIG. 6D, an overcoat layer 250 may be formed on the colorchanging layer 240. Subsequently, the first substrate 100 on which theTFT “T” and the organic electroluminescent layer 160 have been formedand the second substrate 200 on which the color changing layer 240 hasbeen formed may be disposed such that the second passivation layer 180faces the overcoat layer 250. An organic electroluminescent displaydevice may be completed by bonding the first and second substrates 100and 200 together with an adhesive film 300 that adheres the secondpassivation layer 180 to the overcoat layer 250.

[0043] In the present invention, a large organic electroluminescentdisplay device requiring a relatively small amount of power may beobtained by using a thin film transistor to drive the device. Moreover,a high display quality and equal expected life spans for elements may beobtained by forming one organic electroluminescent layer over an entiresurface of a substrate and emitting light through a color changinglayer. Furthermore, the described invention may have the effect ofmaking an organic electroluminescent display device moredamage-resistant because the formation of the thin film transistor andthe color changing layer on different substrates that are later attachedprovides an additional substrate covering the elements to shield themfrom an external impact.

[0044] It will be apparent to those skilled in the art that variousmodifications and variations can be made in the organicelectroluminescent display device and fabricating method thereof of thepresent invention without departing from the spirit or scope of theinvention. Thus, it is intended that the present invention cover themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

What is claimed is:
 1. An active matrix organic electroluminescentdisplay device, comprising: a first substrate and a second substratefacing and spaced apart from each other; a thin film transistor on aninner surface of the first substrate; a first electrode connected to thethin film transistor; an organic electroluminescent layer on the firstelectrode; a second electrode on the organic electroluminescent layer; apassivation layer on the second electrode; a black matrix on an innersurface of the second substrate, the black matrix includes a pluralityof open portions; a color filter layer at the plurality of openportions; a color changing layer on the color filter layer; an overcoatlayer on the color changing layer; and an adhesive film between thepassivation layer and the overcoat layer.
 2. The device according toclaim 1, wherein the color filter layer includes first, second, andthird sub-color filters.
 3. The device according to claim 2, whereineach of the first, second and third sub-color filters corresponds to oneof the plurality of open portions.
 4. The device according to claim 2,wherein the color changing layer includes a first color changing mediumon the first sub-color filter and a second color changing medium on thesecond sub-color filter.
 5. The device according to claim 4, wherein theorganic electroluminescent layer emits blue light.
 6. The deviceaccording to claim 5, wherein the first color changing medium changes acolor of light passing through the medium to red.
 7. The deviceaccording to claim 5, wherein the second color changing medium changes acolor of light passing through the medium to green.
 8. The deviceaccording to claim 4, wherein a sum of a thickness of the first colorchanging medium and a thickness of the first sub-color filter issubstantially equal to a thickness of the third sub-color filter.
 9. Thedevice according to claim 4, wherein a sum of a thickness of the secondcolor changing medium and a thickness of the second sub-color filter issubstantially equal to a thickness of the third sub-color filter. 10.The device according to claim 1, wherein the second electrode includes atransparent conductive material.
 11. The device according to claim 10,wherein the first electrode includes an opaque conductive material. 12.The device according to claim 1, wherein the first substrate comprisesglass and the second substrate comprises plastic.
 13. A method offabricating an organic electroluminescent display device, comprisingsteps of: forming a thin film transistor on a first substrate; forming afirst electrode connected to the thin film transistor; forming anorganic electroluminescent layer on the first electrode; forming asecond electrode on the organic electroluminescent layer; forming apassivation layer on the second electroluminescent layer; forming ablack matrix on a second substrate, the black matrix has a plurality ofopen portions; forming a color filter layer at the plurality of openportions; forming a color changing layer on the color filter layer;forming an overcoat layer on the color changing layer; and bonding thefirst substrate to the second substrate by interposing an adhesive filmbetween the passivation layer and the overcoat layer.
 14. The methodaccording to claim 13, wherein the color filter layer includes first,second, and third sub-color filters.
 15. The method according to claim14, wherein each of the first, second, and third sub-color filterscorresponds to one of the plurality of open portions.
 16. The methodaccording to claim 14, wherein the color changing layer includes a firstcolor changing medium on the first sub-color filter and a second colorchanging medium on the second sub-color filter.
 17. The method accordingto claim 16, wherein the organic electroluminescent layer emits bluelight.
 18. The method according to claim 17, wherein the first colorchanging medium changes a color of light passing through the medium tored.
 19. The method according to claim 17, wherein the second colorchanging medium changes a color of light passing through the medium togreen.
 20. The device according to claim 16, wherein a sum of athickness of the first color changing medium and a thickness of thefirst sub-color filter is substantially equal to a thickness of thethird sub-color filter.
 21. The device according to claim 16, wherein asum of a thickness of the second color changing medium and a thicknessof the second sub-color filter is substantially equal to a thickness ofthe third sub-color filter.
 22. The method according to claim 13,wherein the second electrode includes a transparent conductive material.23. The method according to claim 22, wherein the first electrodeincludes an opaque conductive material.
 24. The method according toclaim 13, wherein the first substrate includes glass and the secondsubstrate includes plastic.